I've done some light schematic building lately, and this mod is by far the easiest and most effective method I've found. It's simple and convenient to use, completely mod/game agnostic (a must for development outside of MTG), and offers reasonably polished presentation.
The only features that feel like they're missing is an option to load schematics registered by mods and a quick way to swap or flood-fill nodes in a schematic, but these are easy to work around or provide externally anyway. Overall, this mod makes for an incredibly useful development tool.
Best way I know to create schematics for your own mods
This mod makes it possible to save and load areas in a Minetest world as schematic files.
With it players can build structures in Minetest and save the result to a file in their world folder.
The mod is easy to understand and does not depend on any game – not even minetest_game.
In my opinion that makes it an excellent choice to create schematics, even for beginner mod developers.
There even exist special nodes for common use cases – for example, when air should not be placed in a schematic.
Saving a schematic:
You place a schemedit node at a corner of the area that you wish to save as a schematic.
You click the node, then specify the area size and filename in a form. The area bounds can be clearly visible.
You click a button to save the area as a schematic. It will be saved in the folder schems, which is located in the folder of the world you created it in.
Loading a schematic:
You put the schematic that you want to load in the folder schems, which should be located in the folder of the world you want it to be in. (Create it if it does not exist.)
You place a schemeedit node at a corner of the the area where you wish to load a schematic.
You click the node, then specify the filename in a form.
Other schematic editors are just not as simple as this mod! I have used this for all of my schematics for more than 3 years now, and can say that I have never run into any problems.
I agree with Hugues, that a function to quickly change nodes within the region would be useful, especially for turning air nodes into void nodes. One can also use Worldedit to accomplish this- it hardly adds any new complication, and is quick & easy to use.
this tool makes ones life way easier when creating schematics (outside of small lua defined ones). it also is game agnostic which is a plus allowing users to use it in any project they may be working on.
This mod remains the go-to tool for creating and editing schematics for Minetest mods and games. Compared to schematic editors that are external programs, this mod relies on Minetest itself for modifying the schematics once imported, making the process of building and modifying schematics simple and effectively providing support for any game made both in the present or in the future.
This is the mod that made schematics accessable to me. The system is simple, and wonderfully free from dependencies. For modders and anyone who needs to create or view schematics this is the best option I've found.